Method for increasing surface adhesion in polyetherimide substrates

ABSTRACT

A process of enhancing surface adhesion of polyetherimides for metal plating includes contacting sulfuric acid with a surface of a polyetherimide substrate for a first dwell time to form a pre-etched polyetherimide substrate, contacting the pre-etched polyetherimide substrate with a mixture of sulfuric acid and periodate ions for a dwell time to form an oxidized polyetherimide surface, contacting the oxidized polyetherimide surface with an alkaline metal hydroxide solution for a third dwell time without rinsing between the applying steps or between the applying and contacting steps, where the polyetherimide is free of or includes a low volume percentage of reinforcement particles, and the process does not include contacting the polyetherimide substrate with nitric acid in any step.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. Provisional Patent Application No. 62/911,834, filed on Oct. 7, 2019, the contents of which are incorporated herein by reference in their entirety.

FIELD

The present technology is generally related to plating technology for plastic substrates. More specifically, it is related to improving the surface adhesion of metal plated layers on polyetherimide (PEI) substrates with and without reinforcement particles.

BACKGROUND

In some aerospace industries, like aircraft production or space ship flight vehicles, polyetherimide molded or fabricated parts are considered as an alternative to a metallic plated metal substrate component for their weight reducing properties. However, to be considered as a viable alternative, these polyetherimide parts are designed to meet stringent flight hardware requirements. An example such requirements is the ability to operate in a wide range of service temperatures (e.g. extremes of cold and hot). In these service environments, any functionally plated coatings onto the polyetherimide substrate must be able to maintain their adherence to the base substrate due to differences in thermal expansions between the plated layers and the base substrate. This is important for the non-conductive substrate plated for the purpose of maintaining the electrical conductivity of plated layers to the substrate in case of wire breakage, and the necessity to ground electrical energy. Additionally, multilayer metal coatings are required to adhere to the substrate to maintain their functionality (e.g. corrosion resistance or for non-reflectivity of the part). Therefore, polyetherimide molded parts are plated to meet some or all these service requirements, as well as, to have excellent adhesion of multilayer plated coatings. This allows polyetherimide molded parts to perform equally well in the same harsh conditions as the metallic based substrate components are expected to operate with the advantage of reduced weight.

The state of the art for plating polyetherimide molded parts start with a preliminary surface that is mechanically roughened (e.g. abrasive blasting) in order to enhance the adhesional characteristics of subsequently plated layers. However, even after using both a combination of abrasive blasting, followed by further chemical roughening (currently using a hexavalent chromium based etching treatment), the percentage of rejected parts due to adhesion failure observed after simulated service conditions (e.g. thermal cycling parts between −54 C to 180 C) of parts using the prior art approaches nearly 50-70%.

It has also been known since the 1980's to treat polyetherimide substrates with concentrated sulphuric acid as a “mild” etching solution (see e.g. U.S. Pat. Nos. 4,873,136; 4,999,251; 4,999,251; 4,959,121) to increase adhesion of plated metallic layers onto the substrate. The use of such “mild” etching on polyetherimide is considered the main adhesional pre-treatment operation to alter the surface of the substrate. Other surface treatment teachings in prior art are used to clean the polyetherimide surface from a non-adherent film that has formed during the “mild” etching process.

Recently, an adhesion pretreatment method for plastics (including polyetherimide composites) has been described and is based on a pre-treatment with concentrated nitric acid followed by etching solutions of periodate ions in concentrated sulphuric acid (U.S. Patent Publication No. 2017/0073816, “the '816 Publication”). This method demonstrates that various metallic layers (nickel, copper, electroless nickel, etc.) may be plated onto an electroconductive layer on Ultem 2300 (30% of glass fibers) surface. However, the degree of adhesion by this method may be susceptible to the volume fraction or percentage of reinforcement particles (e.g. glass fiber) present in the molded part. If the polyetherimide molded part contains a low percentage of glass fibers, for example, in Ultem 6601 (e.g 5% glass fiber) or it is a part molded from a resin free of glass fibers, like Ultem 1000, the method fails to provide sufficient adhesion of multiple plated layers that could meet the stringent service conditions when simulated by thermal cycling.

The reduced adhesion is likely due to reaction products forming on the substrate from their reaction with periodate are dissolving gradually and diffusing into the bulk solution. This is visually apparent on the surface of the substrate which turns a dark color than the original molded part. Additionally, the reinforcement particles (e.g. glass fibers) within the PEI substrate are partially exposed and further serve to act as anchor-holding points for deposited metal layer, thereby increasing overall adhesion of the plated layers. For those PEI substrates that contain negligible (i.e. less than 5 volume percent) amounts of reinforcement particles, there is no significant increase in total adhesion due to less anchoring points.

SUMMARY

In one aspect, a process of enhancing the surface adhesion of polyetherimides for metal plating, the process including for the first etching treatment contacting sulfuric acid with a surface of a polyetherimide substrate (instead of being contacted with concentrated nitric acid) for a first dwell time (to form a pre-etched surface) followed by contacting the pre-etched polyetherimide substrate with a second etching treatment mixture of sulfuric acid and periodate ions (for a second dwell time) to form an oxidized polyetherimide surface; then contacting the oxidized polyetherimide surface with an alkaline metal hydroxide solution (for a third dwell time) without rinsing between the applying steps or between the applying and contacting steps; wherein the polyetherimide comprises a low volume percentage of reinforcement particles, and the process does not include contacting the polyetherimide substrate with nitric acid in any step.

In some embodiments of the process, the reinforcement particles may include a metal, a metal oxide, a metal carbide, a metal nitride, a metal boride, carbon, carbon fibers, carbon nanotubes, graphene, fullerene, graphite, graphite fibers, glass, glass fibers, fiberglass, metal-coated glass fibers, metal-coated carbon fibers, metal-coated graphite fibers, talc, calcium silicate, silica, calcium carbonate, alumina, titanium dioxide, ferrite, mica, mixed silicates, or a mixture of any two or more thereof. In any of the above embodiments, the reinforcement particles may include glass fiber, fiberglass, a metal-coated fiber, a mineral filler, or a combination of any two or more thereof.

In any of the above embodiments, a concentration of the sulfuric acid may be from 84 wt % to 97 wt %. In any of the above embodiments, the first dwell time may be from 2 to 30 minutes. In any of the above embodiments, the second dwell time may be from 4 to 30 minutes. In any of the above embodiments, a concentration of alkaline metal hydroxide in the alkaline metal hydroxide solution may be from 0.2 M to 1.0 M. In any of the above embodiments, the third dwell time may be a minimum time of 3 minutes.

DETAILED DESCRIPTION

Various embodiments are described hereinafter. It should be noted that the specific embodiments are not intended as an exhaustive description or as a limitation to the broader aspects discussed herein. One aspect described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced with any other embodiment(s).

As used herein, “about” will be understood by persons of ordinary skill in the art and will vary to some extent depending upon the context in which it is used. If there are uses of the term which are not clear to persons of ordinary skill in the art, given the context in which it is used, “about” will mean up to plus or minus 10% of the particular term.

The use of the terms “a” and “an” and “the” and similar referents in the context of describing the elements (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the embodiments and does not pose a limitation on the scope of the claims unless otherwise stated. No language in the specification should be construed as indicating any non-claimed element as essential.

It has now been found that polyetherimide (PEI) surface adhesion for plating with metallic coatings may be improved by pretreatment of the surface with the methods described herein. Plated polyetherimide surfaces may be used in industrial settings where the coatings have either a decorative purpose (e.g. for color, or brilliance), or as a functional metallic coating (e.g. corrosion resistance, electrical conductivity, etc.) on a part made from a polyetherimide resin. A typical industrial application for polyetherimide plated components is for the aerospace connector industry. In this application, a lighter weight plated polyetherimide component is used to replace a similar component in size and shape made from a metallic base material (e.g. steel or aluminum) to reduce the overall weight of the assembly.

In one aspect, a chrome-free adhesion pretreatment process for preparation of reinforced or unreinforced polyetherimide substrates prior to metallization is provided. The pretreatment process includes contacting the polyetherimide substrate with concentrated sulphuric acid followed by etching with a mixture of sulphuric acid of same concentration and periodate ions. The process does not require preliminary mechanical surface roughening (e.g. abrasive blasting) for adhesion to occur prior to metallization. The processes are particularly amenable to polyetherimide substrates having a low volume percentage of reinforcement particles. As used herein, “a low volume percentage,” refers to a polyetherimide having from 0 to 5 vol % (volume percentage) of reinforcement particles.

Illustrative reinforcement particles may include, but are not limited to a metal, a metal oxide, a metal carbide, a metal nitride, a metal boride, carbon, carbon fibers, carbon nanotubes, graphene, fullerene, graphite, graphite fibers, glass, glass fibers, fiberglass, metal-coated glass fibers, metal-coated carbon fibers, metal-coated graphite fibers, talc, calcium silicate, silica, calcium carbonate, alumina, titanium dioxide, ferrite, mica, mixed silicates, or a mixture of any two or more thereof. In some embodiments, the polyetherimide substrate may include glass fibers, metal-coated fibers, mineral fillers, or a combination of any two or more thereof.

Sources of periodate (IO₄ ⁻) ions may be any periodate source. Illustrative sources of periodate include but are not limited to lithium periodate, sodium periodate, potassium periodate, lithium hydrogen periodate, sodium hydrogen periodate, potassium hydrogen periodate, and periodic acid.

The process includes contacting a polyetherimide substrate with sulfuric acid having a concentration from 84 wt % to 97 wt % for a first dwell time to form a pre-etched polyetherimide substrate. The pre-etched polyetherimide substrate is then subsequently, and without rinsing, contacted with a solution of sulfuric acid having a concentration of 84 wt % to 97 wt % and periodate ions having a concentration of 0.03 to 0.2 M/L for a second dwell time to form an etched polyetherimide molded part. Finally, the etched polyetherimide substrate is contacted, i.e. washed, with a 0.2 M to 1.0 M alkaline metal hydroxide solution (i.e. LiOH, NaOH, KOH, or a mixture of any two or more thereof) for a third dwell time. As noted above, the polyetherimide substrates are those molded parts made of polyetherimide and having a low volume percentage of reinforcement particles.

In the process, the dwell times may be of any effective range. For example, the first dwell time may be from greater than 0 second to about 1 hour. This includes from about 1 minute to about 60 minutes, from about 2 minutes to about 60 minutes, from about 1 minute to about 45 minutes, from about 2 minutes to about 45 minutes, from about 1 minute to about 30 minutes, or from about 2 minutes to about 30 minutes. In the process the second dwell time may be from greater than 0 second to about 1 hour. This includes from about 1 minute to about 60 minutes, from about 5 minutes to about 60 minutes, from about 5 minutes to about 45 minutes, from about 5 minutes to about 30 minutes, from about 1 minute to about 30 minutes, or from about 5 minutes to about 15 minutes. In the process the third dwell time may be from greater than about 1 minute. This includes greater than about 2 minutes, or greater than about 3 minutes. The third dwell time may be from about 1 minute to about 60 minutes, from about 2 minutes to about 60 minutes, from about 3 minutes to about 60 minutes, from about 1 minute to about 30 minutes, from about 2 minutes to about 30 minutes, or from about 3 minutes to about 30 minutes. In general, the dwell time of the etching in the sulfuric acid and periodate solution may be adjusted to correspond with prior treatment dwell time of the sulfuric acid alone. During the dwell time of the etching in the sulfuric acid and periodate solution a visually perceptible, non-adherent film is formed. However, the film can be sufficiently removed in the following cleaning operation with the metal hydroxide solution as described below. The reaction times, of course, and the amount of the non-adherent film that is formed are determined by the dwell time in the first etcher and the concentration of periodate ions in the second etcher.

After etching in the solution of sulfuric acid and periodate, there is formed a non-adherent insoluble film on the surface of the polyetherimide substrate. The film is likely the reaction byproduct of the polyetherimide substrate with both the sulfuric acid and the periodate ions. The byproduct, due to its non-adherent nature, should be removed from the polyetherimide surface, otherwise, during subsequent metallization and plating the rest of part resulting the presence of this film can result in poor adhesion during thermal cycle testing. This invention shows that this non-adherent film can be dissolved in alkaline metals hydroxides containing water at ambient temperature. Illustrative alkaline metal hydroxide solutions based on NaOH or KOH may be used for solution make-up. The solution concentration of the NaOH or KOH is typically not less than 0.2M and subsequent rinsing times in water of not less than 3 minutes is recommended. The higher the NaOH or KOH concentration, the less rinsing times are required for the particles to be completely removed from the polyetherimide surface. However, NaOH or KOH concentration above 1M is not recommended since the higher the hydroxide concentration are, the greater the propensity for CO2 absorption in the solution from the ambient air atmosphere.

Visual color observations of the polyetherimide substrates with periodate ions directly allows for evaluation of how various factors (e.g. temperature, acid concentrations, periodate concentration, etch dwell time, among others) influence reaction rate during etching. We have found that using “mild” etching treatments of polyetherimide substrates first with pure concentrated sulphuric acid drastically increases polyetherimide surface modification when followed by contacting the same polyetherimide substrate (without rinsing) with sulphuric acid of the same concentration containing periodate ions. This mechanism can be explained by the fact that the reaction with periodate is so vigorous that reaction products dissolving in surface boundary layer next to solution/substrate interface inhibit the newly etched polyetherimide surface from further reacting with fresh bulk etch solution thereby generating a polyetherimide surface with greater roughness.

When comparing the prior art teachings described above, particularly with regard to the '816 Publication (i.e. where the first treatment is in concentrated nitric acid followed by second treatment of concentrated sulfuric acid with periodate) to the present process, the present process provides for significantly improved etching. The significantly improved etching is evidenced by visual examination of parts prepared by both methods, where the present process provides a part that is much less light reflective (e.g. a more roughen surface). Furthermore, by examining thermal cycling results of the comparative parts (i.e. the prior art parts v. those prepared by the present processes), the chemical activity of the periodate in the present treatment is enhanced by pre-treating with the concentrated sulfuric acid without periodate as the first step compared to pre-treatment with concentrated nitric acid. The higher adhesional values in the present polyetherimide substrates (with low volume fraction of reinforcement particles) can be attributed to the first treatment increasing the chemical activity of the PEI substrate that upon reaction with the periodate ions (in the following etching solution) this results in enhanced surface modification and increasing surface roughness. It is this increased surface roughness that is the main mechanism of increased adhesion in polyetherimide composites with low volume fractions of reinforcement (e.g. glass) particles.

When comparing the present process and parts prepared therefrom to the process and parts described in the '816 Publication, the present process is more environmentally friendly than the use of nitic acid in terms of worker toxicity and less vapor emission during use, and less water is used during the present process by eliminating the intermediate rinsing steps.

The present invention, thus generally described, will be understood more readily by reference to the following examples, which are provided by way of illustration and are not intended to be limiting of the present invention.

Examples

General. Aircraft electrical cable connector bodies of one type molded from Ultem 1100 (glass fiber free) and Ultem 6601 (5 wt % glass fibers) and also connectors bodies of another type molded from Ultem 2300 (30 wt % glass fibers) are used to demonstrate the advantage of the proposed periodate based adhesion pretreatment method for polyetherimides to compare with the process described in the '816 Publication. Each variation of adhesion pretreatment is applied for 100 polyetherimide pieces. After that, the pieces are covered with multilayer plating which is usually used for electrical cable connectors. Finally, plated pieces are subjected to plating adhesion quality evaluation procedure to define number (percentage) of pieces that meet the requirements for metal plating adhesion to polyetherimides.

Example 1. Adhesion pretreating step. First, polyetherimide pieces are degreased. As used herein, the term “degreased” means the polyetherimide surface is either free of or cleaned to be free of molding oils, fingerprints, and other surface impurities. The degreasing procedure is executed using a standard alkaline cleaner. Degreasing time for this example is about 20 minutes at about 60° C. Degreasing is followed by rinsing with tap water for 1 minute and then drying.

The polyetherimide pieces are then subjected to contact either with 60 wt % HNO₃ for 10 minutes (according to the '816 Publication) or with sulfuric acid at a fixed concentration for a fixed duration (according to present process). After that, the pieces are either rinsed with water, dried, and dipped into 0.2 M sodium periodate solution in sulfuric acid (according to the '816 Publication), or are placed directly (without rinsing) from sulfuric acid to a solution of sodium periodate in sulfuric acid (according to proposed method). The sulfuric acid is the same as the sulfuric acid acid used to dissolve the sodium periodate. The pieces are etched by the sodium periodate for a fixed amount of time and then are removed and rinsed with tap water for 2 minutes. The pieces are then cleaned by rinsing them for a fixed amount of time in a room temperature sodium hydroxide solution at a fixed concentration, and they are then finally rinsed with tap water for 1 minute.

Example 2. Ni plating of a polyetherimide. For the Ni layer being deposited, the polyetherimide pieces first are treated in a room temperature solution containing 20 g/L of CoCl₂.6H₂O at a pH of about 6.5 for 2 minutes. The pieces are then rinsed with deionized water and dipped for 1 minute into a room temperature solution containing 10 g/L of Na₂S and 30 g/L of NaOH. The pieces are again rinsed with water and electroplated with a Ni layer using a conventional Watt's Ni plating bath containing 200 g/L of NiSO₄.7H₂O, 40 g/L of NiCl₂.6H₂O, and 40 g/L of H₃BO₃ at 45° C. using a current density 2 A/dm² for 10 minutes.

After being plated with a layer of Ni, the pieces are rinsed with water and further are electroplated with 16 mkm of copper using an electrolyte containing 150 g/L of CuSO₄.5H₂O and 150 g/L of sulfuric acid. The plating is held for 50 minutes at ambient temperature without agitation using current density of about 1.5 A/dm².

Finally, the pieces are plated with about 7 mkm of electroless Ni layer using Coventya low phosphorus electroless nickel EF 245. Plating is executed at 90° C. for 35 minutes. Before electroless plating, the copper-plated pieces are activated by depositing onto Cu layer near 0.8 mkm of Ni from a Watt's bath during 4 minutes at 1 A/dm². After being plated with electroless Ni, the pieces are rinsed with deionised water and dried.

Example 3. Evaluation of the adhesion of the nickel layer. One hundred polyetherimide pieces were treated in the above manner and then subjected to multi thermoshock testing using a Thermatron S-4-8200 machine. The pieces were kept 30 minutes at −54° C., then heat at 177° C. for 30 min. The cycle is performed 3 times: 1) subject plated parts treated by the invention above, cool parts for 30 minutes at −54 C, 2) transfer the cold parts within 2 minutes to an oven set at 177° C. for 30 minutes, 3) repeat same thermal cycle of cooling then heating for 3 times, and 4) visual examination of parts for blistering, peeling, cracking or delamination of any plated surface from the polyetherimide substrate. Then the pieces are carefully inspected for any defect of metal plating (stripping, blistering, etc). The number of unaffected by multi thermoshock test pieces is defined. Various conditions of adhesion pretreatment and corresponding data for the number of unaffected by multi thermoshock test polyetherimide pieces are provided in Table 1.

TABLE 1 Thermoshock testing results. Contacting with Contacting with Rinse in NaOH Glass HNO₃ H₂SO₄ Etching by periodate in H₂SO₄ solution % of fibers HNO₃ Time H₂SO₄ Time H₂SO₄ Time NaIO₄ NaOH Time pieces passed Example polyetherimide (wt %) (wt %) (min.) (wt %) (min.) (wt %) (min.) (M) (M) (min.) thermoshocks  1 Ultem 2300 30 60 10 — — 92  4 0.2 — —  78  2 Ultem 2300 30 — — 92  4 92  4 0.2 — — 100  3 Ultem 6601  5 60 10 — — 92  4 0.2 — —  10  4 Ultem 6601  5 — — 92 10 92  4 0.2 0.2 5  96  5 Ultem 1000  0 60 10 — — 92 20 0.2 — —  5  6 Ultem 1000  0 — — 92 10 92 20 0.2 0.2 3 100  7 Ultem 1000  0 — — 86 30 86 30 0.2 0.2 5  90  8 Ultem 1000  0 — — 83 30 83 30 0.2 0.2 5  6  9 Ultem 1000  0 — — 92  2 92 20 0.2 0.2 5  65 10 Ultem 1000  0 — — 97  2 97  5 0.2 0.2 5  96 11 Ultem 6601  5 — — 92 10 92  1 0.2 0.2 5  37 12 Ultem 6601  5 — — 92 10 92 20 0.2  0.05 5  50 13 Ultem 6601  5 — — 92 10 92 20 0.2 0.2 1  80

Process embodiment results discussion. The data shown in Table 1 suggest that the preliminary contacting of the polyetherimide with concentrated sulphuric acid yields metallized polyetherimide that exhibit superior results (Examples 2, 4, and 6) compared to contacting of the part first with concentrated nitric acid (Examples 1, 3, and 5). The superior results are based upon adhesional results extrapolated by subjecting all example treated parts through the same environmental thermal cycle service environment. Improved results in the case of preliminary contact with sulphuric acid are for the Ultem 2300 parts (i.e. a high glass fiber content; compare examples 1 and 2), for Ultem 6601 which contains a low amount of glass fibers (compare examples 3 and 4) and for Ultem 1000 which is free of glass fibers (compare examples 5 and 6).

In the case of a polyetherimide with a high concentration of glass fibers, however, the difference in results between HNO₃ and H₂SO₄ pre-treatment is less pronounced than in the low glass fiber or glass-fiber free examples. The results of sulfuric acid contacting, followed by etching with sulfuric acid and periodate are better as the H₂SO₄ concentration increases (compare examples 6, 7, and 8). At a concentration of about 83 wt %, even if the polyetherimide contacting with H₂SO₄ dwell time is 30 minutes, the pre-treatment effectiveness drops sharply (example 8). At higher acid concentration the result are improved, even when employing a shorter dwell time (example 10). Etching with periodate duration should correspond to contacting with H₂SO₄ duration and if it is too short (example 11), the result is not satisfactory (compare examples 4 and 11). It is also shown in Table 1 that the polyetherimide cleaning in the alkaline solution also may influence the final result. Lower alkaline concentrations (example 12) and shorter rinsing durations (example 13) reduce the number of quality plated polyetherimide parts (compare with example 4).

Para. 1. A process of enhancing surface adhesion of polyetherimides for metal plating, the process comprising: contacting sulfuric acid with a surface of a polyetherimide substrate for a first dwell time to form a pre-etched polyetherimide substrate; contacting the pre-etched polyetherimide substrate with a mixture of sulfuric acid and periodate ions for a second dwell time to form an oxidized polyetherimide surface; contacting the oxidized polyetherimide surface with an alkaline metal hydroxide solution for a third dwell time without rinsing between the applying steps or between the applying and contacting steps; wherein the polyetherimide comprises a low volume percentage of reinforcement particles, and the process does not include contacting the polyetherimide substrate with nitric acid in any step.

Para. 2. The process of Para. 1, wherein the reinforcement particles comprise a metal, a metal oxide, a metal carbide, a metal nitride, a metal boride, carbon, carbon fibers, carbon nanotubes, graphene, fullerene, graphite, graphite fibers, glass, glass fibers, fiberglass, metal-coated glass fibers, metal-coated carbon fibers, metal-coated graphite fibers, talc, calcium silicate, silica, calcium carbonate, alumina, titanium dioxide, ferrite, mica, mixed silicates, or a mixture of any two or more thereof.

Para. 3. The process of Para. 1 or 2, wherein the reinforcement particles comprise glass fiber, fiberglass, a metal-coated fiber, a mineral filler, or a combination of any two or more thereof.

Para. 4. The process of any one of Paras. 1-3, wherein a concentration of the sulfuric acid is from 84 wt % to 97 wt %.

Para. 5. The process of any one of Paras. 1-4, wherein the first dwell time is from 2 to 30 minutes.

Para. 6. The process of any one of Paras. 1-5, wherein the second dwell time is from 4 to 30 minutes.

Para. 7. The process of any one of Paras. 1-6, wherein a concentration of alkaline metal hydroxide in the alkaline metal hydroxide solution is from 0.2 M to 1.0 M.

Para. 8. The process of any one of Paras. 1-7, wherein the third dwell time is a minimum time of 3 minutes.

While certain embodiments have been illustrated and described, it should be understood that changes and modifications can be made therein in accordance with ordinary skill in the art without departing from the technology in its broader aspects as defined in the following claims.

The embodiments, illustratively described herein may suitably be practiced in the absence of any element or elements, limitation or limitations, not specifically disclosed herein. Thus, for example, the terms “comprising,” “including,” “containing,” etc. shall be read expansively and without limitation. Additionally, the terms and expressions employed herein have been used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the claimed technology. Additionally, the phrase “consisting essentially of” will be understood to include those elements specifically recited and those additional elements that do not materially affect the basic and novel characteristics of the claimed technology. The phrase “consisting of” excludes any element not specified.

The present disclosure is not to be limited in terms of the particular embodiments described in this application. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and compositions within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods, reagents, compounds, compositions, or biological systems, which can of course vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.

As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” and the like, include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member.

All publications, patent applications, issued patents, and other documents referred to in this specification are herein incorporated by reference as if each individual publication, patent application, issued patent, or other document was specifically and individually indicated to be incorporated by reference in its entirety. Definitions that are contained in text incorporated by reference are excluded to the extent that they contradict definitions in this disclosure.

Other embodiments are set forth in the following claims. 

What is claimed is:
 1. A process of enhancing surface adhesion of polyetherimides for metal plating, the process comprising: contacting sulfuric acid with a surface of a polyetherimide substrate for a first dwell time to form a pre-etched polyetherimide substrate; contacting the pre-etched polyetherimide substrate with a mixture of sulfuric acid and periodate ions for a second dwell time to form an oxidized polyetherimide surface; contacting the oxidized polyetherimide surface with an alkaline metal hydroxide solution for a third dwell time without rinsing between the applying steps or between the applying and contacting steps; wherein the polyetherimide comprises a low volume percentage of reinforcement particles, and the process does not include contacting the polyetherimide substrate with nitric acid in any step.
 2. The process of claim 1, wherein the reinforcement particles comprise a metal, a metal oxide, a metal carbide, a metal nitride, a metal boride, carbon, carbon fibers, carbon nanotubes, graphene, fullerene, graphite, graphite fibers, glass, glass fibers, fiberglass, metal-coated glass fibers, metal-coated carbon fibers, metal-coated graphite fibers, talc, calcium silicate, silica, calcium carbonate, alumina, titanium dioxide, ferrite, mica, mixed silicates, or a mixture of any two or more thereof.
 3. The process of claim 1, wherein the reinforcement particles comprise glass fiber, fiberglass, a metal-coated fiber, a mineral filler, or a combination of any two or more thereof.
 4. The process of claim 1, wherein a concentration of the sulfuric acid is from 84 wt % to 97 wt %.
 5. The process of claim 1, wherein the first dwell time is from 2 to 30 minutes.
 6. The process of claim 1, wherein the second dwell time is from 4 to 30 minutes.
 7. The process of claim 1, wherein a concentration of alkaline metal hydroxide in the alkaline metal hydroxide solution is from 0.2 M to 1.0 M.
 8. The process of claim 1, wherein the third dwell time is a minimum time of 3 minutes. 